The present invention relates to a camouflage material for multi-spectral camouflage including protection from radar observation, comprising a layer-shaped backing material with a pile of textile or synthetic fibres or loops of mainly unequal lengths and lying in different directions, said fibres or loops being fixed to the backing material for example by weaving, embedding or tufting, whereby provision is made of filament or threadlike pieces that affect radar waves, for example carbon or metal threads or metal coated synthetic fibres.
To camouflage objects or constructions against radar observation, for example from the air, it is known that materials can be used which absorb part of the radar signals - and thereby hinder or at least reduce reflections of these signals from the camouflaged object-, or materials which reflect incident radar signals in different directions so that an observer is deceived, or eventually a combination of absorptive or reducing materials and reflecting or scattering materials is used.
For example, from U.S. Pat. No. 3,733,606, a camouflage material is known in which a foil, that constitutes part of a multi-layered material, forms a conducting thin layer in the form of a metallic grid of threads or metallized fibres of synthetic material. Such threads or fibres, which can have a diameter of about 8 microns, or slightly more, and lengths of 7-16 cm, can be irregularly distributed in a layer of synthetic material or needle felt, that can be combined with one or more other layers which are dyed or treated to achieve optical camouflage, camouflage in the infrared spectrum and eventually also give a reduction of radar signal reflections.
In this way a certain camouflage effect is achieved, which can be improved if the material is provided with slits and stretched so that after stretching a so-called three-dimensional structure results which also improves the radar camouflage effect, partly due to scattering of the radar signals, partly due to an increase in radar energy losses by ohmic and dielectric losses.
This known camouflage material and in particular its single layers has little thickness, e.g. about 0.5 mm in all, and the aforementioned metal threads are substantially all lying in one and the same plane, which results in a severe limitation with respect to scattering of the incoming and reflected radar signals. A not inconsiderable amount of the radiation can be assumed to be reflected towards the radar receiver, which facilitates a certain usage of the radar return.
From U.S. Pat. No. 3,599,210 a radar wave absorbing coating is known, in the form of a lossy dielectric resin binder within which there is embedded randomly distributed conducting fibres, of a length corresponding to one half of the wavelength of the expected radar radiation. These fibres function as resonantly tuned dipoles, when the coating is irradiated with radar signals having the wavelength, to which said fibres are tuned, and an electromagnetic energy loss occurs in the lossy binder.
This known coating, that only protects against radar observation, but hardly offers any considerable protection against visual observation, i.e. does not result in a multi-spectral camouflage, is obviously only suited--and intended--to be used for the protection of aircrafts, missiles and the like against radar observation, whereas it is not suited to be used for the protection of fixed installations and objects or for use in terrain, partly because it does not offer any multispectral camouflage, partly due to its construction which has low mechanical strength and for example does not tolerate traffic, particularly vehicular traffic. Furthermore this known coating has a drawback in that the embedded fibres always hold one and the same orientation, and they cannot be supplemented or replaced with fibres of a different length if the radar frequency should be different from the one expected. In such case there could arise an undesirable and consistent reflection pattern.
From U.S. Pat. No. 4,287,243 and corresponding Danish Patent Specification No. 144954 a camouflage material is known of the previously described type, with material that affects radar waves, consisting of radar wave absorbing fibres or carbon particles and/or locally embedded metal particles or a metal net reflecting radar waves such that a decoy effect is produced. This known camouflage material exhibits by way of its pile construction a considerable mechanical strength and an effective multi-spectral camouflage effect; but a more diffuse and varied scattering and a stronger attenuation of radar waves is desirable in many cases.
The present invention it is intended therefore to produce a similar robustly constructed and universally applicable camouflage material, which by simple means affords not only an effective multi-spectral camouflage, also in the themal, the optical and the near infrared range, but, in addition, also a much improved protection against radar observation.